Current analyzers, as used routinely in chemical analysis, in forensics, in microbiology and in clinical diagnostics, are capable of carrying out a multiplicity of detection reactions and analyses with a multiplicity of samples. To be able to carry out a multiplicity of tests in an automated manner, there is a need for various automatically functioning devices for the spatial transfer of measurement cells, reaction vessels and reagent liquid containers, such as, for example, transfer arms with gripper function, transport belts or rotatable transport wheels, and also devices for the transfer of liquids, such as, for example, pipetting devices. The instruments comprise a central control unit which, by means of corresponding software, is capable of planning and working through the work steps for the desired analyses in a largely autonomous manner.
Many of the analytical methods used in such automatically functioning analyzers are based on optical techniques. Especially widespread are measurement systems based on photometric (e.g., turbidimetric, nephelometric, fluorometric or luminometric) or radiometric measurement principles. These methods allow the qualitative and quantitative detection of analytes in liquid samples without the need to provide additional separation steps. The determination of clinically relevant parameters, such as, for example, the concentration or the activity of an analyte, is done in many cases by simultaneously or successively mixing an aliquot of a body fluid from a patient with one or more test reagents in a reaction vessel, initiating a biochemical reaction which brings about a measurable change in an optical property of the test volume.
The measurement result is forwarded in turn by the measurement system to a storage unit and evaluated. Thereafter, the analyzer delivers sample-specific measurement values to a user via an output medium, such as, for example, a monitor, a printer or a network connection.
The transfer of sample liquids or of reagent liquids is typically achieved using automated pipetting devices. Such pipetting devices generally comprise a pipetting needle which is arranged perpendicularly on a shiftable transfer arm and is adjustable in height and which is connected to a pump unit, and so it is possible by means of the pipetting needle to remove a desired volume of a liquid from a container and to dispense it at another location into a target container. Typically, the pipetting needle is shifted by means of the transfer arm to a position above a liquid container and then lowered into the liquid container and the liquid present therein. After removal of the desired volume, the pipetting needle is driven upward and then, by means of the horizontally shiftable transfer arm, driven to the desired target position above a liquid container, for example above a reaction vessel or a measurement cell. There, the pipetting needle is again lowered, and the quantity of liquid is dispensed.
It is known that pipetting inaccuracies may arise as a result of portions of a liquid volume dispensed by a pipetting needle continuing to adhere on the pipetting needle tip owing to adhesion forces. This can have severe consequences especially when pipetting volumes in the microliter range, if this yields an incorrect composition of a reaction volume and generates faulty measurement results.
To avoid such pipetting inaccuracies, attempts are typically made to pipette the liquid volume onto the vessel inner wall, so that an adhesion of the liquid on the pipetting needle tip is avoided.
In the prior art, pipetting needles having slightly curved tips are used to this end, for example. However, this has the disadvantage of limited usefulness, since, for example, such pipetting needles cannot be used even to pierce tube caps.
In another method for avoiding air bubbles when adding a reagent liquid to a sample liquid, the pipetting operation is controlled such that the pipetting needle is lowered into a reaction vessel in a vertical direction and in a central manner, and is then shifted in a horizontal direction, such that the tip of the pipetting needle touches the perpendicular inner wall of the reaction vessel lengthwise in a perpendicular manner, and in this position the liquid volume is then dispensed (WO-A1-2015/079829).